Numerous rod-shaped bacterial pathogens are capable of adopting a highly filamentous morphology during infection. Filamentation is caused by the arrest of bacterial cell division, with ongoing DNA replication, cell growth and elongation. One such human pathogen, Uropathogenic Escherichia coli (UPEC), which accounts for up to 90% of all urinary tract infections (UTIs), undergoes extensive filamentation during late stage bladder infection leading to bladder cell rupture, evasion of immune phagocytes, and avid binding to surfaces of the urinary tract. It has become clear that this morphological transformation is an essential, tightly regulated survival strategy providing a selective advantage for UPEC within UTIs. However, despite its pathogenic importance, the mechanisms underlying the filamentation response remain unclear.
Using UPEC as a model for pathogenic bacterial filamentation, we have developed a novel, high-throughput genome-wide screen that has identified UPEC genes involved in reversible filamentation. Firstly, a plasmid-based genomic expression library containing genes from UPEC strain UTI-89 was constructed. Controlled expression of the cloned genes was induced, and bacteria that developed a filamentous phenotype were isolated using flow cytometry sorting. Plasmid DNA was then sequenced using Illumina MiSeq high-throughput technology, and eighty-six loci were found to be significantly enriched in the filamentous-sorted population. This has revealed genes with a known involvement in cell division, as well as many new discoveries. Our results establish a novel link between central carbon metabolism and cell division inhibition in E. coli. Of particular interest also was the identification of many phage-associated genes suspected to be involved in blocking cytokinesis, seemingly as a strategy that aids phage proliferation and egress. Additionally, we identified several uncharacterised proteins which have great potential to underlie the specific filamentation response seen in UTIs.